Abstract
Measuring the maximal number of heel-rises is the clinical standard to quantify plantarflexor strength. However, this activity can be difficult and uncomfortable after Achilles tendon rupture (ATR) and may capture aspects other than muscle strength and endurance. Therefore, the aim of this study project was to evaluate muscle fatigue with a limited number of heel-rises. Fifty-two patients with ATR were evaluated 2.0-6.7 years after injury. Patients performed the heel-rise test with surface electromyography (sEMG) of the gastrocnemius muscles. Muscle fatigue was operationally defined as the slope of the sEMG signal frequency. Subjects performed significantly fewer heel-rises on the injured side compared with the uninjured side (25.5 ± 9.3 vs 33.6 ± 15.1; p < 0.001). Subjects also had greater muscle fatigue on the injured side compared with the uninjured side for the lateral gastrocnemius (−31.1 ± 13.9 vs -26.2 ± 14.8; p = 0.048), but not the medial gastrocnemius (p = 0.074). There was a significant increase in fatigue of both the lateral and medial gastrocnemius on the injured side over the first 10 repetitions (p < 0.001). Our findings demonstrate that subjects have increased gastrocnemius muscle fatigue even several years after ATR and muscle fatigue can be detected with a limited number of heel-rises.
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